1. Field of the Invention
The present invention relates to a novel curable composition and more particularly to a light- or heat-curable composition soluble in organic solvents.
In recent years, extensive studies have been made to develop heat-resistant, thermosetting or photosensitive macromolecular materials for use as electronic or optical components. Such components include: surface-protecting films, e.g. junction coatings, passivation films, buffer coatings, and .alpha.-ray shielding films; insulation films for semiconductor devices, e.g. insulation films between layers for multilayer circuits; molecular-oriented films for liquid crystal display devices; and insulation films for thin-film magnetic heads or for multilayer printed circuit boards.
2. Description of the Prior Art
A heat-resistant thermosetting composition (Japanese Patent Application Laid-Open No. 179242/82) comprises a polyamide acid or polyamide acid ester that is a polyimide precursor. This composition is used to form, for example, an insulation film between layers in the following manner: A solution of the polyimide precursor is applied on a substrate and dried; a positive type of photoresist is applied on the precursor layer and dried; the photoresist layer is irradiated with actinic rays, such as ultraviolet rays, through a photoresist, and developed together with the polyimide precursor layer by using a basic developing solution; after the photoresist has been developed by using an organic solvent, the whole layer is heated at a temperature of about 400.degree. C. to convert the precursor into the final product polyimide. Heat-resistant photosensitive compositions are also known to shorten the process by requiring no photoresist. Such compositions include, for example, (1) a polymer produced by introducing active functional groups, such as double-bond containing groups, onto the ester side chains of a polyamide acid, which is a polyimide precursor and (2) a composition comprising a mixture of a polyamide acid with an amine compound having an active functional group, such as a double-bond containing group (Japanese Patent Publication Nos. 30207/80 and 41422/80 and Japanese Patent Application Laid-Open Nos. 168942/82 and 145794/79). This type of composition, containing a photosensitizer and a photopolymerizable monomer, is used to form, for example, an insulation film between layers in the following manner: a solution of the composition is applied on a substrate; after drying, the obtained coating is irradiated with actinic rays through a photomask, developed to form an image and imidized by heating at a temperature of about 400.degree. C.
However, the noted prior-art compositions, comprising a polyimide precursor, require heat treatment at a temperature of about 400.degree. C. in order to form a heat-resistant polyimide films or heat-resistant patterns of polyimide. Another drawback of these compositions is the weak adhesion of polyimides to substrates, which results from the large shrinkage of polyimide precursors in the heat treatment. Moreover, these compositions have problems in that the volatile matter present in the precursor tends to produce microvoids in the resulting polyimide film, and the thermal expansion coefficient of the film is still large since the film is not crosslinked.